The present invention relates to a temperature control device for a semiconductor laser.
Generally, the output of a semiconductor laser varies widely with variations in its temperature, even when the current is kept constant. Therefore, maintaining this output at a constant level necessitates controlling the temperature as well as the current. Conventionally, a Peltier element is used to control the temperature of the semiconductor laser. That is, when one of the metal plates of the Peltier element contacts the semiconductor laser, the polarity of the current supplied to the Peltier element is varied in accordance with the variation in temperature of the semiconductor laser. Thus, the direction of heat transmission between the Peltier element and the semiconductor laser is varied, whereby the laser is heated or cooled, with the result that the temperature thereof is kept constant. In this way, controlling the temperature of the laser using the Peltier element necessitates the provision of two types of power source: one, a power source of negative polarity, and the other, a power source of positive polarity. Conventionally, a power source (.+-.12.about.15 V) for an analog circuit section is used as a power source for the Peltier element. However, since the voltage consumed by the Peltier element is around .+-. 2 V, using a power source having a voltage of .+-.12.about.15 V results in a voltage of 10.about.13 V being uselessly consumed by heat dissipation. For this reason, the efficiency with which the power source is utilized decreases. On the other hand, since the power source voltage for a digital circuit section is as low as +5 V, the use of this power source makes it possible to enhance the power source efficiency. However, such a power source for a digital circuit can usually supply only a voltage of positive polarity, and so the necessity arises to provide a separate power source of negative polarity, resulting in a complicated structure.